1. Field of Invention
The invention relates to novel fluid compositions for use in an electrophoretic display device, electrophoretic display devices containing such display fluids, and methods of displaying images with the electrophoretic display devices.
2. Description of Related Art
Electrophoretic displays, also more commonly referred to as electronic paper, are well known in the art. An electrophoretic display generally comprises a suspension of a single type of charged pigment particles colloidally dispersed in a colored liquid of matching specific gravity contained in a cell comprising two parallel and transparent conducting electrode panels. The charged particles are transported between the electrode panels under the influence of an electric field, and can therefore be made to display an image through appropriate application of the electric field on the electrodes. The advantages of electrophoretic displays as a means for providing information and displaying images has been well appreciated in the prior art.
U.S. Pat. No. 4,272,596, incorporated herein by reference in its entirety, illustrates a typical electrophoretic display structure. The electrophoretic display device comprises a pair of electrodes associated so as to form a cavity therebetween, which cavity is filled with an electrophoretic suspension layer comprising a colored suspending medium containing colloidal sized particles in an electrically insulating liquid and finely divided electrophoretic particles suspended in the suspending medium. A source of electrical potential is coupled to the electrodes and with an electric field applied, the marking particles form an image as they follow the field. See especially FIG. 1 therein.
U.S. Pat. No. 6,113,810 describes a dielectric dispersion for use in an electrophoretic display that includes a dielectric fluid, a first plurality of particles of a first color having a surface charge of a selected polarity dispersed within the dielectric fluid and a second plurality of particles of a second color having a surface charge of opposite polarity to that of the first plurality and a steric repulsion thereto preventing coagulation of the first and second pluralities. In one embodiment, the first and second plurality of particles is each formed by separate two stage dispersion polymerization reactions. Each set of particles is formed with unique secondary and functional monomers. Corresponding charge control agents are added to the dispersion to establish opposite polarities on the respective particles.
U.S. Pat. No. 6,017,584 discloses encapsulated displays, i.e., displays in which the electrophoretic fluid is encapsulated within a microcapsule. This fluid may be a mixture of two or more fluids or may be a single fluid. The displays may further comprise particles dispersed in a suspending fluid, wherein the particles contain a liquid. In either case, the suspending fluid may have a density or refractive index substantially matched to that of the particles dispersed therein. Application of electric fields to any of the electrophoretic displays described therein is indicated to affect an optical property of the display.
While improvements have been made in the field of electrophoretic displays, many problems still need to be addressed in order for electronic paper applications to move toward large commercial scale production and use. For example, quality and resolution of the display devices can continue to be further improved.
It is thus an object of the present invention to develop novel electrophoretic display fluids that are improved in operation and exhibit improved image quality and resolution when used in an electrophoretic display device.
It is a still further object of the present invention to develop improved methods of operating an electrophoretic display device to obtain higher quality and higher resolution images.
These and other objects are achieved by the present invention, which in embodiments is directed to an electrophoretic display device comprising a multiplicity of individual reservoirs, each containing an electrophoretic display fluid, located between two conductive film substrates, at least one of which is transparent, wherein the electrophoretic display fluid comprises two sets of particles dispersed in a transparent liquid system, the two sets of particles exhibiting different, contrasting color and different charging properties from each other, and wherein at least one of the sets of particles are emulsion/aggregation particles.
In other embodiments, the invention is also directed to particle design that the density of particles are adjustable from about 0.85 cm3/g to about 3.5 cm3/g with varied resin to pigment ratio during particle preparation, and the particle size distribution is narrow with geometric standard deviation (GSD) of from, for example, about 1.05 to about 1.35, and the roughness of the particle surface and the shape of the particles are adjustable during the preparation process, and the effective surface area (calculated by total surface area divided by volume) is adjustable by the surface roughness and is about 1 to about 100 times higher than the spherical particles, and the pigment exposure on the particle surface is adjustable during the particle preparation to minimize the interference of charging by pigment on the particle surface.
In other embodiments, the invention is also directed to an electrophoretic display device comprising a multiplicity of individual reservoirs, each containing an electrophoretic display fluid, located between two conductive film substrates, at least one of which is transparent, wherein the electrophoretic display fluid comprises two sets of particles dispersed in a transparent liquid system, the two sets of particles exhibiting different, contrasting color, and wherein at least one of the sets of particles are magnetic particles while the other set of particles are non-magnetic particles.
In other embodiments, the invention is also directed to an electrophoretic display device comprising a multiplicity of individual reservoirs, each containing an electrophoretic display fluid, located between two conductive film substrates, at least one of which is transparent, wherein the electrophoretic display fluid comprises two sets of particles dispersed in a transparent liquid system, the two sets of particles exhibiting different, contrasting color and different charging properties from each other, and wherein at least one of the sets of particles are hollow polymer particles. Preferably, the hollow polymer particles are white in color while another set of particles is darkly colored particles.
In other embodiments, the invention is also directed to an electrophoretic display device comprising a multiplicity of individual reservoirs, each containing an electrophoretic display fluid, located between two conductive film substrates, at least one of which is transparent, wherein the electrophoretic display fluid comprises two sets of particles dispersed in a transparent liquid system, the two sets of particles exhibiting different, contrasting color, and wherein at least one of the sets of particles are colored particles encapsulated within a metal oxide shell.
The invention is also directed to an electrophoretic display device comprising a multiplicity of individual reservoirs, each containing an electrophoretic display fluid, located between two conductive film substrates, at least one of which is transparent, wherein the electrophoretic display fluid comprises two sets of particles dispersed in a transparent liquid system, the two sets of particles exhibiting different, contrasting color and different charging properties from each other, wherein the transparent liquid system comprises two immiscible liquids having different densities such that the immiscible liquid having a density less than that of the other immiscible liquid rests on top of the other immiscible liquid, and wherein the sets of particles have densities in between the densities of the two immiscible liquids such that the particles rest at an interface between the two immiscible liquids.
The invention still further relates to an electrophoretic display device comprising a multiplicity of individual reservoirs, each containing an electrophoretic display fluid, located between two conductive film substrates, at least one of which is transparent, wherein the electrophoretic display fluid comprises one set of particles dispersed in a colored liquid system, the particles exhibiting different, contrasting color to the color of the liquid, and wherein the particles are emulsion/aggregation particles. In a related embodiment, the colored liquid system comprises two immiscible liquids having different densities such that the immiscible liquid having a density less than that of the other immiscible liquid rests on top of the other immiscible liquid, and wherein the sets of particles have densities in between the densities of the two immiscible liquids such that the particles rest at an interface between the two immiscible liquids.